FIELD OF THE INVENTION
The present invention relates to a glass composition suitable for substrates for display devices such as fluorescent character display tubes, plasma display panels, flat cathode ray tubes and liquid crystal display tubes.
As a glass substrate for plasma display, a soda lime glass having a strain point of about 510.degree. C., formed by float process, is commonly used. A typical plasma display panel is produced by the following process.
Firstly, on a glass substrate for the display surface side, display electrodes will be printed, and dielectric layer will be printed thereon, followed by baking. Further, a protective film will be vapor-deposited on this dielectric layer. On the other hand, on the opposing rear-side glass substrate, Al, Ag or Ni electrodes, and stripe-shaped partition walls (low melting point glass) to prevent electric discharge between electrodes and to prevent color mixing of red-, green- and blue-phosphors, will be formed by baking at a temperature of from 500.degree. to 600.degree. C. Further, printed circuits will be formed, and red-, green- and blue-phosphors will be printed.
The display side and rear side glass substrates will be bonded by means of a low melting temperature glass frit within the same temperature range as the above-mentioned temperature, and a gas mixture of xenon and neon as the main discharge gas, will be sealed in to obtain a plasma display panel.
The glass substrate for plasma display is subjected to heat treatment at a temperature equal to or higher than the strain point of soda lime glass at a level of from 500.degree. to 600.degree. C., and thermal deformation is likely to take place. Therefore, when soda lime glass substrates are used, a 40 inch panel is almost at the limit, and it is substantially difficult to use soda lime glass substrates for high definition TV which requires a panel of a larger size with a high level of resolution.
A ZrO.sub.2 -containing glass is also known which undergoes a less degree of deformation by such heat treatment (Japanese Unexamined Patent Publication No. 40933/1991). However, this glass is susceptible to scratching, and it is necessary not to polish the glass or to polish with a due care not to form a substantial scratch mark. Further, even with a glass having no scratch mark, a scratch mark may form during the production process. Therefore, a due care will be required for handling in the process.
Each of these methods reduces the amount of glass substrate which can be produced per unit period of time. In other words, each method has a problem that the production cost of glass increases.